1. Field of the Invention
The present invention relates to a hermetically sealed fuel tank apparatus having a fuel tank for storing a fuel and a canister for adsorbing a fuel vapor in the fuel tank.
2. Description of the Related Art
It is known in the art that a fuel tank is used to supply a fuel to an internal combustion engine on a motor vehicle. While the fuel is stored in the fuel tank, the fuel evaporates into a fuel vapor. To prevent the fuel vapor from dissipating from the fuel tank into the atmosphere, a canister is combined with the fuel tank to trap the fuel vapor.
The canister is filled with an adsorbent such as activated carbon particles for trapping the fuel vapor by way of adsorption. When the internal combustion engine starts to operate, the fuel vapor trapped by the canister is purged through a purge passage into the intake passage of the internal combustion engine. Since the trapped fuel vapor is purged into the intake passage, breakthrough (flowing out) of the fuel vapor from the canister drain is reduced.
There is known in the art a failure diagnosing apparatus for a fuel vapor purge system as disclosed in Japanese Laid-Open Patent Publication No. 2004-156468, for example. The fuel vapor purge system combined with the disclosed failure diagnosing apparatus has a canister disposed in a fuel tank and an evaporation path including the canister and the fuel tank. A fuel vapor produced in the fuel tank is trapped by the canister. The fuel vapor trapped by the canister is purged through a purge passage into the intake passage of an internal combustion engine that is combined with the fuel tank. In the fuel vapor purge system, the failure diagnosing apparatus operates to diagnose a leakage failure of the fuel vapor from the evaporation path.
The failure diagnosing apparatus includes an air delivery means for delivering a gas which is present in either one of the fuel tank and the canister to the other of the fuel tank and the canister, and a determination means for determining a leakage failure of the fuel vapor from the evaporation path based on the difference between the internal pressure of the canister and the internal pressure of the fuel tank when the gas delivery means is in operation.
Japanese Laid-Open Patent Publication No. 2005-016406 reveals an apparatus for controlling a hermetically sealed fuel tank system including a fuel tank for storing a fuel, a canister for adsorbing an evaporated fuel in the fuel tank, a vapor passage interconnecting the fuel tank and the canister, and a control valve for selectively opening and closing the vapor passage. When the control valve is closed, the fuel tank is hermetically sealed. As the fuel tank starts being supplied with the fuel, the control valve is opened. The control apparatus includes a control means for temporarily closing the control valve after the fuel tank starts being supplied with the fuel, and determining whether the fuel tank is being supplied with the fuel or not based on a pressure change in the fuel tank which is responsive to the closing of the control valve.
If the internal combustion engine has not been started over a long period of time, then the fuel vapor is purged from the canister much less frequently. In a hybrid vehicle system which employs an internal combustion engine and a motor in combination, it is desirable that the canister be hermetically sealed to reduce breakthrough of the fuel vapor from the canister.
According to Japanese Laid-Open Patent Publication No. 2004-156468, the canister communicates with the atmosphere through an atmosphere inlet passage which has an atmosphere shutoff valve. Since the atmosphere shutoff valve is normally open, the canister is not of a hermetically sealed structure. Consequently, if the fuel vapor is purged from the canister infrequently, then breakthrough of the fuel vapor from the canister tends to increase.
According to Japanese Laid-Open Patent Publication No. 2005-016406, the canister is disposed outside of the fuel tank, and is likely to fail to have a sufficient pressure strength to resist the hermetically sealing pressure to which the canister is subjected. Therefore, the canister may not be able to hold the activated carbon particles securely and may suffer performance failures due to the insufficient pressure strength.